Since its introduction to the United States in the late 1970's, glass ionomer cements have gained a great deal of popularity for use in various dental procedures. The interest in using glass ionomer cements for a myriad of purposes stems from the cement's ability to bond to both dentin and enamel, the fact that the cement is tooth-colored when hardened, and because glass ionomer cements generally contain fluorides which are thought to minimize the occurrence of decay to the tooth surface to which the glass ionomer cement is applied. Initially, glass ionomer cements were generally used for restorations. These glass ionomer cements, known as Type II glass ionomer cements, are of a larger particulate matter than are the Type I glass ionomer cements used for other purposes. When these Type II glass ionomer cements are used as a restoration material, the lesion in a tooth is prepared by standard techniques as may be performed for cavity preparation for the placement of an amalgam restoration thereon; however, it may not be necessary to create an undercut for a glass ionomer restoration. Care must be taken to make certain that the preparation is free of moisture as glass ionomer cement in such an application is extremely susceptible to water contamination and dehydration during the initial setting stage.
Type I glass ionomer cements are typically used as a base, liner, or luting agent. When used for these purposes, the surface of the tooth again must be substantially free from moisture during application as well as throughout the hardening process of the glass ionomer cement. In addition to its use as restorations, base, liner or luting agent, glass ionomer cements are also used for affixing restorations to a tooth. For composite restorations, such as ceramic or porcelain prostheses, the glass ionomer cement is allowed to harden and then is etched before placement of the composite restoration thereon. For those restorations containing metal, the glass ionomer cement need not be hardened first as wet glass ionomer cement is known to adhere to cast metals.
Glass ionomer cements are generally comprised of a powder component containing aluminosilicate and a liquid portion. Often the liquid portion is expressed as containing polyacrylic acid, polymaleic acid, polyitaconic acid, or a copolymer of at least two of the acids. The liquid portion may also comprise carboxylate polymers or carboxylic acid polymeric structures, such as those including acrylic acid, maleic acid, crotonic acid, isocrotonic acid, methacrylic acid, sorbic acid, cinnamic acid, fumaric acids and the like. "New Aspects of the Setting of Glass-ionomer Cements," Wasson et al., Journal of Dental Research; Vol. 72, No. 2, February, 1993; pages 481-483. In all glass ionomer cements, the primary reactions which cause the glass ionomer cement to harden is cross-linking, i.e., the crosslinking of polycarboxylate chains by metal ions from the glass. Also, during setting, the acids of the glass ionomer cement dissolve the glass structure to release metal constituents of the glass. Metal carboxylates are formed during the setting process. This may be distinguished from the primary setting reactions of acrylic cements which are other forms of polymerization reactions. Though other forms of polymerization reactions may occur in glass ionomer cements, these reactions are secondary to the cross-linking reactions of the glass ionomer cement.
Recently, it was discovered that wet glass ionomer cement bonds well with wet amalgam. As disclosed in U.S. patent application Ser. No. 07/942,375, filed Sep. 9, 1992, now U.S. Pat. No. 5,252,122, a dental restoration is formed by applying a layer of wet glass ionomer cement to a lesion in a tooth, placing a layer of wet amalgam directly on the layer of wet glass ionomer cement, and allowing the cement and the amalgam to harden to thereby bond the amalgam to the tooth. Such a restoration is beneficial in that the cavity preparation need not be undercut for the placement of an amalgam restoration. Further, the glass ionomer cement does not appear to be as moisture sensitive in such a procedure. Finally, the creation of the restoration is less time consuming than is a restoration in which the glass ionomer cement is hardened and then etched before the lesion is filled with amalgam.
Because glass ionomer cements have so many appealing qualities to the dental profession, numerous variations of glass ionomer cements have been developed to enhance particular properties of the glass ionomer cements for specific applications. For example, U.S. Pat. No. 4,738,722, discloses a glass ionomer cement containing additives such as zinc oxide and titanium oxide. These additives improve the glass ionomer cement by eliminating pulpal sensitivity and also affect the setting time of the cement. Specifically, reducing the setting time of the cement with the introduction of these additives is beneficial when the glass ionomer cement is used as a base, liner, or luting agent wherein it is desirable to have a quick setting cement for the completion of further procedures thereafter.
In U.S. Pat. No. 4,064,629, large metal particles are added to a glass ionomer cement. In this manner when the cement is used as a base or liner for an amalgam restoration, application of a wet amalgam to a hardened glass ionomer cement essentially results in the cross-amalgamation of the mercury in the amalgam with the large metal particles in the cement. This additive assists in strengthening the bond between the hardened glass ionomer cement base and the amalgam restoration.
Another approach to strengthening the glass ionomer cement without effecting its adhesive properties is disclosed in U.S. Pat. No. 4,738,722. Specifically, manufacturers have been known to add the powder component of an amalgam to the glass ionomer cement. Such an additive may be particularly helpful when using a glass ionomer cement as a restoration. Yet another additive is disclosed in Japanese Patent No. 2,275,731. In this patent, zinc oxide and zirconium oxide are added to the glass ionomer cement to improve its resistance to disintegration and crushing and to improve its hardening time.
Another problem associated with glass ionomer cement is its tendency to shrink as it dries in relation to a reduction in the environmental humidity. In response to this problem, an additive mixture to glass ionomer cement comprising quartz sand, cristobalite flour and zirconium silicate was added in a study discussed in the article "Physical and Mechanical Properties of Glass-Ionomer Cements", Elliott, et al., British Polymer Journal, 1975, 9, 297-306. Though the additive mixture assists in reducing shrinkage in a less humid environment, it was also found to reduce the compressive strength of the cement.
Disclosed in U.S. patent application Ser. No. 07/991,112, filed Dec. 16, 1992, now U.S. Pat. No. 5,273,574, is an additive comprising zircon for use with the wet glass ionomer cement to wet amalgam restorative method of U.S. patent application Ser. No. 07/942,375, now U.S. Pat. No. 5,252,122. The zircon additive, in this application of glass ionomer cement, is thought not to interfere with any of the normal chemical reactions of the glass ionomer cement while allowing the practitioner to adjust the color, handling characteristics, and the setting time of the cement.
In addition to modifying the glass ionomer cement, improvements have been made with regard to the wet glass ionomer cement to wet amalgam bond by mixing an additive to the amalgam. Specifically, in U.S. patent application Ser. No. 07/872,501, filed Apr. 23, 1992, now U.S. Pat. No. 5,252,121, additives from the group of metal salts, metal bases and metal oxides are added to the amalgam to improve such a bond. Such an additive may comprise, for example, the powder component of a polycarboxylate cement.
With each of the various dental procedures for which glass ionomer cements are known to be used, it is desired to improve upon certain characteristics of this cement depending on the particular use of the cement. As previously noted, a relatively quick setting time is desired when the glass ionomer cement is being used as a base, liner or luting agent or when used to affix a composite restoration to a tooth. This desire is based on the requirement for the glass ionomer cement to first harden prior to the completion of subsequent dental procedures. Further, any improvements which can be made for any use of a glass ionomer cement which inhibits secondary caries or which strengthens the glass ionomer cement are generally desirable.
In addition to serving as a restoration, amalgam has been used for a variety of dental procedures. For example, there are instances in which it is desirable to build an amalgam post or an amalgam core for attachment of a prosthesis to the tooth. A post is defined as a solid structure which extends into a hole in the tooth, generally a hole formed in the root canal of the tooth. A core extends above the root tooth surface and is generally of larger mass than is a post. Should amalgam be used to build a post or a core, generally, the tooth surface must be undercut to mechanically retain the amalgam within the undercut tooth structure after the amalgam has hardened. Such undercutting is not feasible in all instances depending on the tooth structure remaining and from which the post or core is to extend. Thus, the use of amalgam posts and/or cores may not always be feasible even though desirable for their known strength and adaptability or formability within the tooth. Therefore, it is desired to develop a method for building an amalgam post and/or an amalgam core which does not require undercutting of the remaining tooth structure.
When an amalgam core is used for the application of a prosthesis thereon, difficulty for the dentist and the patient arises in the amount of time usually required for the completion of such a procedure. First, in many instances this involves a multi-step process whereby the core is cemented to the tooth, or, alternately, may involve the application of an amalgam core as previously discussed. In either instance, the core or cement must be allowed to harden. Then, before the prosthesis may be applied to the core with a cement, the core must be properly shaped for the prosthesis or the prosthesis must be made to fit the shape of the core. Again, a period of time expires in treatment. Now, the cement can be used to affix the prosthesis to the core to harden. It is therefore desirable to develop a method for applying both a core and a prosthesis thereon which consumes less time than is currently required.
Another dental procedure to which improvements may be made is that of post cementation. Generally, a hole is prepared in the canal of the tooth for receipt of a post. The cement is spinned or applied into the hole and the post is coated with a cement. The post is then placed into the hole and the cement is allowed to harden such that the cement holds the post's place within the hole. For stainless steel and titanium posts, a variety of cements may be used for this purpose; however, for these posts, cements are known to be deficient to adequately provide the desired rigidity and strength. Therefore, it is desired to provide a method of post cementation that may be utilized with a post of any material to increase the stability with which the post is retained within the hole.
The application of sealants to teeth often poses problems desired to be overcome. In many instances, sealants are applied to a child's teeth with the intent of protecting the tooth. Regardless of the age of the patient, the sealant, usually an acrylic, is applied after etching, rinsing and drying the tooth. The sealant is then allowed to harden. This procedure may take upwards of three minutes to complete. During this period, it is very difficult to isolate moisture from the area to be sealed. Such moisture may reduce the bond between the sealant and the tooth. Therefore, it is desired to develop a procedure for sealing teeth which is less time consuming than the described procedure. In addition, it is desired to provide a sealant which may be used without etching the tooth surface to be sealed. Also, the life expectancy of acrylic sealants is typically five years. There are instances when this period of time is not sufficient and it is therefore desired to develop a sealant having a longer life span. Finally, acrylic sealants do not chemically inhibit the development of secondary caries. Therefore, it is desired to inhibit such decay with the use of a sealant containing fluorides or like decay-inhibiting materials.
There are some instances in which it is desired to splint two teeth together. Such a procedure may be necessary, for example, should a tooth be jarred loose as may be caused by an accident. Generally, the procedure for splinting teeth together today involves cementing the adjacent teeth together by applying crowns thereon. Such a procedure is therefore costly. It is desired, then, to reduce the cost of splinting teeth together as may be necessary to resolve a temporary problem or when the patient is unable to afford a more expensive procedure.
In summary, glass ionomer cements have been used for a variety of purposes since their introduction. Variations on the chemical composition of the glass ionomer cements have proved helpful in the use of glass ionomer cements for particular dental procedures and yet further improvements are desired. In addition, there are numerous dental procedures for which cementing techniques may be utilized and which as currently performed may exhibit difficulties, inconveniences or problems which are desirable to be addressed in the development of new or improved methods.